1. Field of the Invention
The present general inventive concept relates to a hard disk drive, and more particularly, to a recording current optimization method that optimizes a recording current according to a change of a driving voltage applied to a pre-amplifier that generates the recording current supplied to a head, a recording medium storing a program to execute the method, and an apparatus that employs the method.
2. Description of the Related Art
A hard disk drive (HDD) is a recording device used to store information. In general, the information is recorded on concentric tracks in a surface of at least one magnetic recording disk. The disk is mounted on a spindle motor to be rotated, and the information is accessed by a reading/recording head mounted on an actuator arm rotated by a voice coil motor (VCM). The VCM is excited by current and rotates an actuator to move the head. The head senses a magnetic change generated from the disk surface to read the information recorded on the disk surface. In order to record data on the track, current is supplied to the head. The current generates a magnetic field, and the magnetic field magnetizes the disk surface.
A recording density can be increased by reducing a distance between the head and the disk. This reduces the size of the head and positions the head closer to the disk. However, as the distance between the head and the disk is reduced, adjacent tracks may be overwritten by the magnetic field generated in the head, and data recorded in the adjacent tracks may be erased as a result. This phenomenon is called adjacent track erasure (ATE). ATE becomes a critical matter when a recording current supplied to the head is large. On the other hand, weak write (WW) may occur at a low temperature due to an increase in coercivity of the disk surface.
Accordingly, a method of controlling recording parameters of a HDD (for example, a DC current or an over shoot current (OSC) of the recording current) by measuring the temperature of the HDD (by measuring the temperature of a pre-amplifier) has been used.
FIG. 1 is a waveform diagram illustrating a recording current Iw supplied to a head of an HDD. Referring to FIG. 1, a polarity of the recording current Iw is changed at a position where a value of data recorded on a disk is changed. In other words, the recording current Iw changes at the position where a direction of a magnetic field is changed, and an OSC occurs at the position where the direction of the magnetic field is changed. The position where the magnetic field is changed is represented by two arrows in the disk of FIG. 1 extending in opposite directions. A DC component of the recording current Iw retains the intensity of the magnetic field near coercivity. Coercivity, also called a coercive field, of the disk is a measure of the intensity of an applied magnetic field required to reduce the magnetization of the disk to zero after the magnetization of the disk has been driven to saturation. The OSC serves as a trigger for increasing the intensity of the magnetic field more than coercivity at the position at which the direction of the magnetic field for writing is changed.
FIG. 2 illustrates the operation of a pre-amplifier. The pre-amplifier generates the recording current having the waveform corresponding to the data to be written as illustrated in FIG. 1. The recording current generated by the pre-amplifier is applied to the head. Although a single waveform is illustrated in FIG. 1, in actuality, a pair of differential currents corresponding to the recording current Iw illustrated in FIG. 1 is applied to both ends of the head.
The pre-amplifier is a voltage source that supplies the recording current Iw to a head through a resistance(s). That is, the pre-amplifier sets the DC component and the OSC of the recording current by changing the resistance(s). The pre-amplifier includes a register to set the DC component of the recording current and a register to set the OSC of the recording current. A controller (not illustrated) controls the DC component and the OSC of the recording current by setting values of the registers.
Referring to FIG. 2, a driving voltage Vp applied to the pre-amplifier is the sum of a positive driving voltage VCC and a negative driving voltage VEE. However, as described above, since the pre-amplifier serves as the voltage source, the recording current supplied to the head is changed according to a change in the driving voltage VP applied to the pre-amplifier. This means that, even when the registers of the pre-amplifier are set by the controller, the recording current is changed as the driving voltage VP of the pre-amplifier changes. A head launch voltage VLAUNCH is applied across a head load of the head to produce the recording current Iw flowing through the head load. The head launch voltage VLAUNCH across the head load is varied due to the change in the resistance(s), thereby also varying the recording current Iw flowing through the head load.
FIG. 3 is a waveform diagram illustrating a change of the OSC of the recording current Iw according to a change of the head launch voltage VLAUNCH of FIG. 2. In FIG. 3, reference numerals 302, 304, and 306 represent waveforms for which the head launch voltage VLAUNCH is 6.02 V, 6.57 V, and 7.12 V, respectively. Referring to FIG. 3, it can be seen that the OSC of the recording current Iw is changed according to the change in the head launch voltage VLAUNCH.
FIG. 4 is a waveform diagram illustrating a change of the OSC of the recording current Iw according to the change of the driving voltage Vp of FIG. 2 applied to the pre-amplifier. In FIG. 4, reference numerals 402, 404, and 406 represent waveforms for which the driving voltage Vp is 7.32 V, 8 V, and 8.68 V, respectively. Referring to FIG. 4, it can be seen that the OSC of the recording current Iw is changed according to the change in the driving voltage Vp applied to the pre-amplifier.
FIG. 5 illustrates a change in the OSC of the recording current Iw according to a change of the DC component of the recording current Iw. Numeral 502 at the left side of FIG. 5 represents a case in which the recording current Iw is 50 mA while numeral 504 at the right side of FIG. 5 represents a case in which the DC component of the recording current Iw is 25 mA. In each case, a change in the OSC is illustrated when an OSC setting value (OSA) is varied from 0 to 15. Referring to FIG. 5, it can be seen that the OSC is changed as the DC component of the recording current Iw changes even though the OSA is identical.
A maximum value IwPEAK of the recording current Iw is generated at a maximum OSA. In addition, an amplitude of the recording current Iw is determined by an available head launch voltage VAVAILABLE, an impedance RHEAD of the recording head, an output impedance RPA of the pre-amplifier, an interconnection impedance RINTERCONNECT, a length of a transmission line, and a reflection coefficient, but is approximated using the following equation.
            I      ⁢                          ⁢              w        PEAK              ]    ⁢            V      AVAILABLE                      R        HEAD            +              R        PA            +              R        INTERCONNECT            
The available head launch voltage VAVAILABLE is dependent on the driving voltage Vp of the pre-amplifier. For example, if a reference positive driving voltage Vccref of the pre-amplifier is 5 V and a reference negative driving voltage Veeref is −5 V, the available head launch voltage VAVAILABLE1 is about 7 V. If a positive driving voltage Vcc of the pre-amplifier is 5.5 V and a negative driving voltage Vee is −5.5 V, the available head launch voltage VAVAILABLE2 is about 8 V.
Accordingly, a variation ΔIwPEAK of the maximum recording current Iw according to a change of the driving voltage VP of the pre-amplifier is calculated using the following equation.
      Δ    ⁢                  ⁢    I    ⁢                  ⁢          w      PEAK        =                              V                      AVAILABLE            ⁢                                                  ⁢            2                          -                  V                      AVAILABLE            ⁢                                                  ⁢            1                                      V                  AVAILABLE          ⁢                                          ⁢          1                      ⁢                  ⁢                  =                                        8            ⁢                                                  ⁢            V                    -                      7            ⁢                                                  ⁢            V                                    7          ⁢                                          ⁢          V                    =              14.3        ⁢        %            
If the driving voltage VP of the pre-amplifier decreases, the maximum recording current IWPEAK is decreased and the possibility that weak write (WW) occurs is increased. In the opposite case when the driving voltage of the preamplifier increases, the possibility that ATE occurs is increased.
Accordingly, a method and an apparatus that optimizes the recording current Iw according to the change of the driving voltage VP of the pre-amplifier are needed.